Possible New Weapon Against Bacteria / When antibiotics fail, an assault on germs' social life

David Perlman, Chronicle Science Editor

Published 4:00 am, Friday, April 10, 1998

Bacteria that gather by the billions in dangerous and often deadly colonies become highly resistant to antibiotics, but they may yet be defeated by scientists who have discovered the genes that cause formation of the colonies.

The invading bacteria are answering the call of their own genes that signal them to colonize. In effect, they are communicating with each other just as if they were social organisms.

Now three teams of researchers report that they have deciphered the signaling call and believe they are on the track of thwarting the bacteria so the colonies will break up and the microbes will succumb to antibiotic attack.

The bacterial colonies are known as biofilms. They are widely known in nature, from the slippery scum that often forms on rocks in rivers or fouls the hulls of ships to the slimy accumulations of germs that create major infection hazards in hospitals and kill many patients with cystic fibrosis.

Bacteria by themselves or even in small clusters can usually be destroyed by antibiotics, but when the chemical signals produced by their specialized genes tell them to assemble as biofilms, they gather in masses impervious to antibiotics and resistant to other chemicals, including the most powerful detergents.

"Bacteria love to stick, and once they settle down and make a biofilm, it's notoriously difficult to get rid of them," said microbiologist Barbara Iglewski of the University of Rochester, who is one of the report's authors.

The microbe called Pseudomonas aeruginosa is a major killer in hospitals -- particularly among patients with weakened immune systems -- and it can coat catheters, artificial implants and tubes that must carry blood or oxygen to patients.

In the journal Science today, microbiology researchers from the Universities of Iowa and Rochester, as well as Montana State University, are reporting that they have identified the molecule that sends signals to all the multiplying members of an invading Pseudomonas tribe to form themselves into a single complex biofilm, complete with built-in water tunnels carrying nutrition into the cells and funneling waste products out.

The researchers, headed by Dr. E. Peter Greenberg of Iowa, used the Pseudomas microbe as their test organism. In their report in Science, they describe how they have found a single gene that spurs other genes to signal the bacteria to form themselves into biofilms. And in a series of delicate experiments altering the gene, they say, they were able to turn the colony-forming signals on and off -- first creating a biofilm and then causing the film to separate into individual bacteria.

"This is basic research," Greenberg said, "but it leads us into two research directions. It may help find a way to remove a biofilm or make it weaker and more responsive to antibiotics."